Welcome to the Forum! In answer to your question, maybe the first thing to emphasize is that, fortunately, there are no rules in this hobby. How the individual modeler pursues it is entirely his or her business.
I have the impression that lots of modelers - maybe the majority - have more than one pot on the burner at any given moment. Personally, I have two projects under way right now - and, in a typical fit of idiocy, I'm thinking about starting a third one. I suspect I'm fairly typical that way. One particular vessel, or kit, or whatever, grabs my interest for some reason and I feel like I just have to get to grips with it - now.
Your approach - to have two or three models under way simultaneously, at different stages of construction - actually makes a good deal of sense. I work slow (largely because I spend so much of my time these days writing dumb forum posts, rather than out in the workshop where I belong), and on more than one occasion I've found that my fingers and brain have had to relearn certain skills - rigging ratlines and shaping 1/700 photo-etched railings, for instance - because I haven't used them for a long time.
Sometimes I think the hobby might be more rewarding if I forced myself to stick with one project, without interruption, from beginning to end. Maybe I'll actually try that some day, in which case I'll offer Forum readers a full report on the experience. In the mean time, though, for heaven's sake don't feel like your doing anything unusual if you're working on more than one model at a time.
Good luck. It's a great hobby.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.